大兴安岭鄂伦春地区满克头鄂博组火山岩形成年代及地球化学

FORMING AGE AND GEOCHEMISTRY OF THE VOLCANIC ROCKS FROM MANKETOUEBO FORMATION IN OROQEN QI,DAXINGANLING MOUNTAINS

对大兴安岭鄂伦春地区满克头鄂博组火山岩年代学与岩石地球化学特征进行分析,锆石U-Pb测年结果表明火山岩形成时代为晚侏罗世(152.9±1.7 Ma).地球化学特征表明该组火山岩具有富硅、碱,贫钙、镁特征,且具较低Mg~#值及极低的Cr、Co、Ni值的特点.微量元素相对富集大离子亲石元素(LILE)K、Rb、Ba和LREE,亏损高场强元素Nb、Ta、Ti.火山岩具有地壳源区特征,Rb/Sr值平均为0.66,远高于N-MORB(0.03)、OIB(0.047)和E-MORB(0.033),Ti/Zr值平均为13.94,与壳源岩浆的范围(<20)一致,表明该类岩石的原始岩浆起源于地壳岩石的部分熔融.根据岩石地球化学特征,结合区域已有研究资料,本区满克头鄂博组火山岩的形成应与蒙古-鄂霍次克洋向南东方向俯冲作用有关.

The zircon U-Pb dating result indicates that the volcanic rocks from Manketouebo Formation in Oroqen area of Daxinganling Mountains were formed in the Late Jurassic(152.9±1.7 Ma)based on the analysis of chronology and geochemical characteristics of the rocks.The volcanic rocks are characterized by rich Si and alkali,poor Ca and Mg,low Mgand very low Cr,Co and Ni contents,with enrichment of LILEs(K,Rb and Ba)and LREE,and depletion of HFSEs(Nb,Ta and Ti)in trace elements.The volcanic rocks have the characteristics of crust source,with Rb/Sr value of 0.66 averagely,much higher than N-MORB(0.03),OIB(0.047)and E-MORB(0.033).The average Ti/Zr value of13.94 is consistent with the range of crust-derived magma(<20),indicating that the primary magma of volcanic rocks originated from partial melting of crustal rocks.According to the rock geochemical characteristics and regional existing research data,it is considered that the formation of volcanic rocks in the study area is related to the southeastward subduction of Mongolian-Okhotsk Ocean.